Daily Archives: July 24, 2014

Marty Acree was our foreman on the septic project. He had worked on a similar project at the Merced Lake High Sierra Camp. He was an experienced guy. He explained to us how the system was supposed to work.

The problem with building a conventional septic system at 10,000 feet lies in the shallow soil. For a leach field to work, effluent coming down from the vault needs to drip out of the pipes and percolate down through soil or small rocks for purification. This is why before any septic system is approved by local building agencies the owner needs to have a ‘perc’ test performed. This measures the draining ability of the soils. Soils that don’t drain well are not approved for septic systems. There is no site in the world at 10,000 feet that could pass a perc test. There just is not enough soil laying on top of the bedrock up that high.

The engineers who designed the high-country septic system hit upon a creative idea for solving the perc problem. If the effluent will not perc down, why not get it to perc up? The plan was to crush rock for the leach field, push the pipes in through the fill, cover the fill with red lava rock, pile native dirt over the mound, and then plant native flora on top of the dirt. The plants would draw the effluent water up through the roots for nutrients, effectively making it perc ‘up’. Then the water would pass up and out of the plants via evapotranspiration. They crunched the numbers to figure out how much effluent they could expect, and then they calculated how much flora they would need to remove that amount of effluent. They had it all figured out.

Except for one little detail.

Most of the native soil up that high isn’t really soil at all, but decomposing granite, or DG. There aren’t enough nutrients in it to support much life. The engineers were pretty optimistic regarding the amount of flora that could be coaxed into growing on the mound. Decomposing granite isn’t very good at wicking moisture up, either. Water can drain down through it very well, which is why it was great for using on causeway, but water doesn’t want to travel up through it.